1. Field of the Invention
The present invention relates to a 3D image photographing device and, more particularly, to a 3D image photographing device providing two tracks for coupling a camera to produce a 3D image.
2. Description of the Related Art
FIG. 1 is a schematic view of a conventional 3D image photographing device 9 including a track 91 and a sliding carriage 92. The track 91 has a slideway 911, and the sliding carriage 92 is coupled to the slideway 911. The sliding carriage 92 has a coupling portion 921 for coupling a camera. The sliding carriage 92 is able to slide along the slideway 911. The slideway 911 is in a circular arc shape, and the arc shape of the slideway 911 is normally part of a circle with a diameter between 3 meters to 9 meters. In other words, when the sliding carriage 92 slides along the slideway 911, the coupling portion 921 will move along a path having a curvature equal to the curvature of the slideway 911.
In use of the conventional 3D image photographing device 9, a camera is coupled to the coupling portion 921 of the sliding carriage 92, and the sliding carriage 92 is driven to slide from an end of the slideway 911 toward another end thereof. Thus, the camera can take images of an object from different visual angles by shooting along the path in the arc shape, and the images taken from different visual angles can be synthesized to obtain a three dimensional (3D) image by postproduction software. By applying refraction of grating, such as looking at the 3D image through a lenticular diffraction grating, the 3D image can produce visual illusion, and the user tends to gain a stereoscopic effect from the 3D image.
A traditional 3D image is produced by a plurality of manual work steps, including layering, retouching, outlining, etc. Therefore, the conventional 3D image photographing device 9 can produce a 3D image with a shorter time and a lower labor cost. However, the application of the conventional 3D image photographing device 9 is not popular, because the conventional 3D image photographing device 9 can only take clear images of the object located at a single position. Specifically, since the slideway 911 is in the circular arc shape which is part of the circle, the camera keeps focusing on a center of the circle when the camera slides along the slideway 911. Thus, the 3D image produced by the conventional 3D image photographing device 9 only acquires a clear view at the center of the circle. Namely, the conventional 3D image photographing device 9 is incapable of taking clear images of the object at different positions. Any object located away from the center will be out of focus in the 3D image, and, thus, it is difficult to obtain stereoscopic effect from the 3D image.
Moreover, when a distance “D” between the conventional 3D image photographing device 9 and an object to be shot is long, a slideway 911 with a smaller curvature, namely the circular arc shape of the slideway 911 being part of a circle with a larger diameter, is needed. However, the slideway 911 with a smaller curvature will cause the images, that are taken by a camera sliding along the slideway 911, to have similar visual angles. Thus, the slideway 911 has to be long enough in order to obtain a 3D image with satisfactory stereoscopic effect. In fact, if the circular arc shape of the slideway 911 is part of a circle with a diameter of 6 meters, the slideway 911 is normally longer than 1 meter to make sure a radian measure of the images is effectively enlarged. Thus, the size and cost of the conventional 3D image photographing device 9 is high, since the length of slideway 911 is too long. Besides, although a prolonged slideway 911 can increase variation in visual angles of images taken by the camera sliding along the slideway 911, the boundary visual angles of the images will increase accordingly. Thus, the images taken by the camera have a problem of a medium shot offset. An image alignment process is required to correct the medium shot offset, which increases the cost in producing a 3D image.
Furthermore, referring to FIG. 2, the slideway 911 is in the circular arc shape, such that the images taken by a camera coupled to the slideway 911 have a large background offset “d.” Thus, the background of a 3D image obtained from the image will be out of focus. The background offset “d” is particularly large when the length of slideway 911 is long, which leads the 3D image to have a clear object but a fuzzy background, and the performance of the conventional 3D image photographing device 9 is, thus, unsatisfactory.
In view of the foregoing and since the conventional 3D image photographing device 9 has disadvantages, such as the incapability to take clear images of the object at different positions, the difficulty in obtaining a 3D image with a satisfactory stereoscopic effect and a clear background, and the high image production cost as mentioned above, improvement to the conventional 3D image photographing device 9 is necessary.